Membranes have been widely used in chemical analysis methods. Cortes and Davis, U.S. Pat. No. 4,529,521, used membranes to determine components of interest in latex serum. Stevens, Jewett and Bredeweg, U.S. Pat. No. 4,751,004 used membranes to suppress an Ion Chromatography eluent. Morabito, Melcher, Hiller and McCabe, U.S. Pat. No. 4,962,042, used membranes in a Gas Chromatography and Rothman, U.S. Pat. No. 4,837,161, used membranes to add reagent to a Flow Injection Analysis carrier stream. Melcher and Burt, U.S. Pat. No. 4,913,821, used membranes in aphenol analyzer. Melcher and Cortes, U.S. Pat. No. 4,775,476, used membranes in a Liquid Chromatography system. It is known that the protonated or unionized form of an organic acid will permeate across a silicone rubber membrane at a faster rate than the ionized form of the acid.